909 research outputs found
A Pioneering Career in Catalysis: Manfred T. Reetz
No full textIn this invited Account, we highlight the enormous scientific breadth of our mentor Professor Manfred T. Reetz. It stretches from the development of organometallic reagents and transition metal catalysts to the adventurous idea of directed evolution of chemo-, stereo-, and regioselective enzymes, which he considered to be most important. We hope to show that Reetz did not consider these research areas to be totally unrelated realms, and attempt to reveal his transdisciplinary way of thinking about methodology development. Since biocatalysis has become crucial for chemical synthesis, we mainly focus on Reetz's contributions in this area. Some personal reflections from some of his former co-workers are also included, which reveal the stimulating atmosphere in the Reetz group in terms of science, career advice, and the importance of ethical considerations. BT/Biocatalysi
Dyotropic Rearrangements in Organic Solvents, in the Gas Phase, and in Enzyme Catalysis
No full textThis short historical account outlines how Helmut Schwarz and Manfred T. Reetz first met almost half a century ago and remained personal friends ever since. It began by collaborations on dyotropic rearrangements and other transformations in the gas phase. Although their chemical interests diverged considerably over decades, which are briefly mentioned in this account, both were always driven by curiosity. Another common feature was the fact that they both collaborated with Israeli chemists in various projects up to the present day. They also contributed to the celebration in 2015 commemorating 50 years of diplomatic relationship between Israel and Germany
One Hundred Years of the Max‐Planck‐Institut für Kohlenforschung.
No full textThis Essay is an account of the institutional and scientific development of the Max-Planck-Institut für Kohlenforschung in Mülheim an der Ruhr (Germany), which is the successor to the Kaiser-Wilhelm-Institut für Kohlenforschung founded in 1914. The Essay is divided into four main parts, corresponding to the four major periods which are closely associated with the respective Directors of the Institute from 1914 to 2014: 1) Franz Fischer; 2) Karl Ziegler; 3) Günther Wilke; and 4) the period beginning with Manfred T. Reetz, who established a directorate comprising five Directors of equal status, each heading a different research department under the banner of catalysis. Along with key historical events associated with the Institute, research highlights of the four periods are featured
Witnessing the Birth of Directed Evolution of Stereoselective Enzymes as Catalysts in Organic Chemistry
No full textThis invited essay outlines how the idea of directed evolution of stereoselective enzymes was born and implemented experimentally at the Max-Planck-Institut für Kohlenforschung in Mülheim/Germany during the period 1994–1998, a time when Andreas Pfaltz was present in the Institute. As the new and sole director of the MPI, I initiated new research projects, and also started to restructure the Institute with the establishment of five departments, all dedicated to some form of catalysis and to be led by five independent directors. Andreas Pfaltz was the first director whom I hired, heading the Department of Homogeneous Catalysis. During his stay in Mülheim until 1998, the Pfaltz group invented effective chiral ligands for a number of particularly challenging enantioselective transformations. During this period, Andreas Pfaltz witnessed the birth and development of directed evolution of stereoselective enzymes as a new research direction in the Reetz group. Indeed, he was one of the very few organic chemists who realized at the time that a door to a novel research area had been opened. The widespread application of enzymes was hampered for decades due to limited enantio-, diastereo-, and regioselectivity, which was the reason why organic chemists were not interested in biocatalysis. This attitude slowly changed with the advent of directed evolution of stereoselective enzymes in 1997, in a publication from the Reetz group. Methodology development with emphasis on stereo- and regioselectivity as well as activity followed, the techniques and strategies becoming more and more rational. Today, semi-rational approaches and so-called rational enzyme design have merged, as evidenced, inter alia, by the development of focused rational iterative site-specific mutagenesis (FRISM). The toolbox of organic chemists now includes enzymes, primarily because the possibility of controlling stereoselectivity by protein engineering has ensured reliability when facing synthetic challenges
Solubility of hydrogen in single-sized palladium clusters
No full textHydrogen concentration-pressure isotherms of surfactant-stabilized palladium clusters and polymer-embedded palladium clusters with diameters of 2, 3, and 5 nm are measured with the gas sorption method at room temperature. The results show that, compared to bulk palladium, the hydrogen solubility in the a phase of the clusters is enhanced fivefold to tenfold, and the miscibility gap is narrowed. Both results can be explained by assuming that hydrogen occupies the subsurface sites of the palladium clusters. The Pd-H isotherms of all clusters show the existence of hysteresis, even though the formation of misfit dislocations is unfavorable in small clusters. Compared to surfactant-stabilized clusters, the polymer-embedded clusters show slow absorption and desorption kinetics. The absorption kinetics can be described by a diffusion model for the composite polymer-cluster system
Hydrogen and Pd-clusters
No full textIsotherms of Pd-H clusters with different sizes differ from bulk isotherms: they show a largely enhanced solubility in the low-concentration regime. The isotherms resemble those of bulk above the critical point, they show no flat plateau region, but a slope. However, the existence of a hysteresis gives evidence for a phase transition even in small Pd-H clusters. Structural studies of 6.0 nm clusters show a transition between two cubic phases. 3.8 nm Pd-H clusters always show an icosahedral structure in the low and high concentration regime. For an intermediate size of 5.0 nm Pd-H clusters, the lattice structure changes during H-absorption, from cubic to, most probably, icosahedral. The slope in the cluster isotherm's two-phase region is here attributed to stress emerging between the surfactant shell and the cluster during hydrogen-loading. (C) 2003 Elsevier B.V. All rights reserved
Phase transition and lattice expansion during hydrogen loading of nanometer sized palladium clusters
No full textIn situ X-ray diffraction (XRD) measurements for Pd-clusters (3.8 and 6.0 nm) are performed during hydrogen loading and unloading. The lattice parameter increases as a function of the hydrogen partial pressure. The expansion is smaller than that of bulk palladium and is shown to be cluster-size dependent. An (alpha-alpha') phase transition was observed for the large clusters but small clusters do not show this transition. XRD analysis of the as-prepared clusters show that the 3.8-nm sized clusters predominantly have an icosahedral structure, while the 6.0-nm sized clusters have a cubic structure. The effect of size and structure of the cluster on the lattice expansion and on the phase transition will be discussed. (C) 2002 Elsevier B.V. All rights reserved
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